The present invention generally relates to power transmission chains and particularly to an improved guide link for power transmission chains.
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing devices as well as for the transfer of power from the engine to the transmission or the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
Generally, the chain is made from a plurality of individual links positioned side by side to form a row or rank and any number of these rows or ranks are joined together by pivot members to form an endless chain. There may be as few as 60-100 rows of links in a typical chain or as many as 120 rows of links. The number of links in a given row or rank may as few as two or in some cases there may be upwards of 40 positioned adjacent to each other.
Power transmission chains may include those chains especially adapted to connect the pulleys of a variable pulley transmission. The chain generally comprises a plurality of interleaved or laced sets of links with each link having a pair of spaced apertures. The apertures are arranged so that a pivot member joins adjacent sets of links to permit the chain to articulate. Such a chain is generally characterized by the presence of a load block member associated with each sets of links and oriented generally transversely to the links. An example of this type of chain is found in U.S. Pat. No. 5,007,883, which is incorporated herein by reference.
Another type of power transmission chain is referred to as a "silent chain." Conventional silent chains typically include both guide links and inverted tooth links. The guide links hold the chain in alignment on the sprocket and are generally positioned either in the center to fit into a center guide groove in the sprocket or are positioned on the outside edges of alternate sets of links. Guide links typically do not mesh with the sprocket. The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and the sprocket. Each inverted tooth link typically includes a pair of apertures and a pair of depending toes or teeth. Each me is defined by an inside flank and an outside flank. The inside flanks are joined at a crotch. The inverted tooth links are typically designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth links or driving links contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks.
A set or rank of links is assembled from several links positioned alongside of or laterally adjacent to each other. The links are connected by a pivot member, that can be a pin received in the apertures. The pivot member can also comprise a rocker joint, that may include a pair of pins or alternatively, a single pin. Where the rocker joint includes a pair of pins, one of the pins is secured in openings in one of the groups of links and the other pin is secured in openings in the other group of links. Both pins pass through openings in both sets of links, and both pins have arcuate faces for rocking engagement to render the chain flexible. Typically, only one of the pins is secured in the aperture of the guide link while the other pin extends to but not within the aperture of the guide link.
An example of a silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference. An example of a silent chain that can be used in engine timing applications is found in U.S. Pat. No. 4,759,740, which is also incorporated herein by reference.
The silent chain may include a plurality of sets of guide links that flank sets of inside links. To assemble the chain, the apertures of one link set are transversely aligned with one set of apertures of the next adjacent link set. Such an arrangement is commonly known as block lacing. More particularly, the inside links are substantially identical and are placed side-by-side in a row to form a block. Rows or sets of such block laced inside links are preferably alternated with guide link rows. The sets with guide links do not contain any inside links. An example of a block laced chain can be found in U.S. Pat. No. 5,192,253 which is incorporated herein by reference.
Alternatively, the silent chain may include a plurality of guide links that flank interleaved sets of inside links. An example of a silent chain having interleaved sets of inside links can be found in U.S. Pat. No. 4,342,560 referred to above. The inside links are alternately positioned and interconnected by a pivot member that is received by the guide links. Accordingly, one set will be in the so-called guide link row and the other set will be in the so-called non-guide link row.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts. Rotation of a driving sprocket causes power transmission through the chain and a consequent movement of a driven sprocket. A conventional chain drive may include a chain assembly of extended width in order to provide a chain of greater strength. Alternatively, two narrower chain assemblies may be placed side-by-side between pairs of sprockets in order to achieve the equivalent power transmission results as a single extended width chain.
The silent chain drive may also include those chain drives whose driving or inner links are modified as well as the chain sprockets. For example, U.S. patent application Ser. No. 07/885,194 owned by the present assignee and incorporated herein by reference discloses providing a phased relationship between a pair of random or hybrid chain assemblies and a pair of sprockets. The phasing involves modifications to the chain construction, the sprocket construction, and the relationship between the positioning of the chain assemblies and sprockets. The modifications to the sprockets include the use of split sprockets that are phased by one-half tooth, or one-half pitch as well as various other amounts of pitch. The randomization of the sprocket teeth may be in any manner, such as variable spacing, relieved teeth, or tooth elimination.
The modifications to the chain assemblies include randomization by the use of single toe and two toed links in the same or dual chain assemblies as well as the use of link sets of two different configurations, or links of a first set being different from links of a second set. The links of the two link sets may differ in contour, flank configuration, leading inside flank configuration, outside flank configuration, pitch, orientation (as with asymmetrical links, types of driving contact with the sprocket teeth or other types of randomization.
During the operation of power transmission chains in being continuously propelled between a driving sprocket and a driven sprocket, a chain is subjected to many different types of forces, stresses, strains, torque and the like. As the chain moves between the driving sprocket and the driven sprocket, it will be readily understood that when each row of links contacts a sprocket tooth the links in a row will be subjected to forces.
Generally, the pivot members are press fit in the apertures of the guide links and the guide links are fashioned as a solid link without toes and are therefore stiffer than the inner links. Consequently, for a pre-determined load such as in a pre-stress operation, the inner links may be deformed a greater amount than the guide links. This difference in deformation may produce an elongation in the pitch of an inner link that is greater than the outer or guide links causing the pin to bend since the pin is connected to the guide links. As a result, the pivot member may experience greater stress near the guide links causing the pivot member to fracture.
One solution to these problems is identified in U.S. Pat. No. 4,915,675 where the guide links are modified to achieve equal deformation with other inner links within each rank so as to improve the load distribution across each rank. The guide links have less stiffness so that they elongate substantially similarly to the inner links in each of the guide link rows. As a result, elastic deformation of the guide links and the inner links is substantially equal and the pivot members are maintained substantially parallel to each other. U.S. Pat. No. 4,915,675 teaches that this elastic deformation of the guide links and inner links can be made to be substantially the same by configuring the guide link in a kidney-shape and changing its thickness. Depending on the particular lacing pattern chosen for the links, the guide links will have a stiffness of a determined amount less than the inner link stiffness in order to achieve substantially the same elastic deformation as the inner links.
In a like manner, U.S. Pat. No. 2,525,561 shows guide links being shaped in side elevation and dimensioned in cross section so that it has the same elastic properties and the same pitchwise elongation as inner driving links.
Another solution is identified in U.S. Pat. No. 5,176,586 where the rigidity guide links is made to be one-half the rigidity of the other links so that all the links have an equal rate of elongation with respect to the tensile load of the chain. The rigidity is made to be one-half by configuring the guide link with a centrally located window and by modifying its thickness so that it is one-half the thickness of the inner links or by modifying the guide link material so that its Young's modulus of elasticity is one-half that of the inner links or by modifying both the thickness and the material of the guide link.
Similarly, U.S. Pat. No. 4,547,182 shows a chain belt for use in a variable-ratio transmission. The chain belt is constructed in a three-link arrangement where similarly located end portions of a link are offset by two pivot members so that a transverse staggering pattern of the links will repeat for each three links. In order to obtain the same cross-sectional area of the links at any one transverse position, the outer links have one-half the thickness of the inner links. As a result, the sum of the loads placed on the respective links, with respect to the width of the chain and the pivot members, may be balanced depending on the elongation of the respective link elements, when loaded.
Yet another solution is identified in U.S. Ser. No. 08/098,433, filed Jul. 28, 1993 now U.S. Pat. No. 5,345,753 issued Sep. 13, 1994, corresponding to Japanese patent application 4-210144 filed Dec. 7, 1990 and laid open in Japan on Jul. 31, 1992, incorporated herein by reference. In that application, the deformation of the guide links is made equal to the deformation of the inner links. In other words, when a load is applied to the chain, the elongation of the guide link is almost the same as that of the inner links. To achieve equal deformation, the guide link is provided with a center opening, a slit with a curved surface, or two inclined slits.
These solutions may be satisfactory so long as the load on the inner links is less than the yield load of the inner links. If, however, the load on the inner links is greater than the yield load for the inner links, such as during a pre-stress operation, the inner links may be plastically deformed while the guide links are only elastically deformed. In this case, the inner links will attain a "new" pitch, while the guide links, because they were only elastically deformed will resume their original pitch. This difference in pitch may result in residual bending of the pivot member and a decrease in the fatigue strength of the chain strand.
One solution to these problems is to form the guide links so that its pitch is longer than the original pitch of the inner links. Consequently, when the inner links are plastically deformed, their "new" pitch will be substantially the same as the original pitch of the guide links which are only elastically deformed.
The present invention solves these problems by providing an improved guide link for use in a power transmission chain having a yield load that is less than the yield load of the inner links, preferably about one-half less. In this way, the guide links will plastically deform at the same time as the inner links so that the "new" pitch of the inner links and the guide links can be made to be substantially the same. To provide a guide link with a yield load less than the yield load of the inner links, one or more or all of the characteristics of configuration, thickness, or hardness is modified.